The receptor for immunoglobulin E (IgE) mediates reactions of considerable medical interest; in addition it serves as a more general model system for effector systems activated by immunoglobulins. Our basis aim is to understand the early events triggered by this receptor in molecular terms. For this purpose we are determining the structure of the receptor, exploring the early events it activates and ultimately will attempt to understand the structural functional relationships. During the past year the following new results were obtained: 1. Cloning and sequencing of the cDNA for the beta subunit was completed, 2. Cloning and sequencing of the cDNA for the gamma subunit was completed, 3) Expression of the receptor on COS cells transfected with the genes for the three subunits was achieved, 4) The cDNA for the human alpha subunit was cloned and sequenced, 5) A chimeric receptor consisting of the human alpha and rodent beta and gamma chains was expressed on COS cells. 6) The chromosomal localization of the genes coding for alpha, B and gamma begun. Interestingly, the genes for alpha and gamma lie close to the genes coding for Fc gamma receptors. 7) Continued progress in characterizing cytoplasts which show receptor-mediated hydrolysis of phosphoinositides was achieved. The new results open a new era in the investigation of the receptor and should permit a detailed analysis of its structure-function relationships.